The specific aims of this proposal are to achieve a comprehensive understanding, at the cellular and synaptic level, of the functional organization amongst uniquely identified amacrine cells and interneurons that together compute the orientation and direction of visual motion. For the first time since the formulation in the 1950s by Hassenstein and Reichardt of a notional circuit for motion perception, a system of neurons has been identified in the dipteran visual system that supplies motion-sensitive premotor output neurons and has Reichardtian outputs. Arrangements amongst these small-field neurons do not, however, match the expected organization predicted by the Reichardtian model but instead show features suggestive of a Barlow-Levick type detector, in common with directional motion detection circuits in certain mammalian retinas. The architecture of this neuron-based motion-detecting circuit in Diptera differs significantly from previous theoretical "wiring diagrams" in that it reconstitutes directional motion in three successive stages, involving computation of 1) nondirectional motion at the level of amacrine cells, and 2) oriented motion and 3) directional motion at the level of analogues of bipolar and ganglion cells, respectively. Each neuron type participating in the motion-computing pathway is uniquely identifiable using specific antisera, thus allowing its recognition at the light and electron microscopic levels. Intracellular recordings and electron microscopic reconstructions of marked neurons, in conjunction with computational modeling, will be used to test predictions about functional properties and connections. These investigations will elucidate the functional organization of parallel channels that supply subsystems in the optic lobes with information about edge orientation, local figure motion, and other parameters, including stimulus velocity, acceleration, and deceleration. New model circuits based on electrophysiological and synaptic analyses will reveal emerging requirements that will guide future structural and functional studies. This research will provide basic insights into directional motion detection by the dipteran visual system and reveal principles underlying motion detection that transcend phyletic boundaries. It will also lead to the implementation of silicon-based circuits that enable motion detection and shape discrimination and potentially provide the basis for a visual prosthetic device.